Vehicle suspensions

ABSTRACT

A vehicle suspension system includes a hydraulic anti-roll mechanism in which a pair of suspension arms ( 10   a   , 10   b ), on opposite sides of the vehicle, are mounted to the vehicle body pivots ( 16   a   , 16   b ). A pair of hydraulic struts ( 22   a   , 22   b ) are connected between the suspension arms and the body ( 14 ). The struts are asymmetrically mounted so that one is inboard of its suspension arm pivot and the other is outboard of its suspension arm pivot. The two lower chambers of the struts ( 22   a   , 22   b ), through which the connecting rods ( 32 ) of the pistons extend, are hydraulically interconnected, and so are the two upper chambers.

The present invention relates to vehicle suspensions and in particularto the control of vehicle roll.

BACKGROUND OF THE INVENTION

It is known for example from U.S. Pat. No. 4,050,704 to provide avehicle suspension system in which roll, i.e. rotation of the vehicleabout a longitudinal axis parallel to the normal direction of travel, iscontrolled by means of hydraulic cylinders or actuators.

SUMMARY OF THE INVENTION

The present invention provides a vehicle suspension system comprising apair of suspension arms for supporting wheels on opposite sides of avehicle, each suspension arm being pivotably attached to a vehicle body,and a pair of struts each arranged for connection between one of thesuspension arms and the vehicle body to control rotation of thesuspension arm about its respective pivot thereby to control verticalmovement of the respective wheel relative to the vehicle body, whereineach strut comprises a cylinder and a piston which together define aworking chamber, the, piston being movable relative to the cylinder tochange the volume of the working chamber, the two working chambers areinterconnected with each other, the struts are asymmetrically arrangedand the cross sectional areas of the pistons and the distances betweenthe struts and the respective pivots are arranged such that equalvertical movements of the wheels in the same direction produce equal butopposite changes in volume of the respective working chambers.

Preferably the pistons have equal effective working areas and the strutsare connected to the suspension arms at equal distances from therespective pivots. However, provided the product of the working area ofthe piston and the distance between the pivot axes and the point ofattachment of the strut to the suspension arm is the same on each sideof the vehicle, equal wheel movements on each side of the vehicle willresult in equal changes in volume of the respective working chambers andtherefore equal volumes of fluid displacement on each side of thevehicle.

Preferably each piston has a front side and a back side and is connectedto one of the body and the suspension arm by a connecting rod extendingfrom the back side of the piston, wherein the working chambers are onthe same side of the respective pistons. This enables identical strutsto be used on both sides of the vehicle.

More preferably each piston divides its cylinder into first and secondworking chambers the two first working chambers having the sameeffective cross sectional area and being interconnected and the twosecond chambers having the same effective cross sectional area and beinginterconnected. This means that some fluid leakage around the pistonbetween the working chambers is acceptable.

Conveniently one of the struts is connected to its suspension arminboard of its pivot and the other is connected to its suspension armoutboard of its pivot, and the struts are preferably arranged on thesame side of the suspension arms and are at least substantially parallelFor example both the struts may be arranged to operate in use in asubstantially vertical direction and may be arranged above thesuspension arms. However it will be appreciated that the orientation ofeither of the struts can be chosen by choosing the direction at whichthe part of the suspension arm to which they are attached extends fromthe pivot. For example one or both of the struts can be arrangedhorizontally if it acts on a part of the suspension arm vertically abovethe axis of the respective pivot.

At least one of the pairs of interconnected clambers may be connected toa source of fluid pressure and control means provided to control theflow of fluid to and from said pair of chambers to control actively rollof the vehicle.

BRIEF DESCRIPTION THE DRAWINGS

Preferred embodiments of the present invention will now be described byway of example only with reference to the accompanying drawings inwhich:

FIG. 1 is a diagrammatic representation of part of a vehicle suspensionsystem according to a first embodiment of the present invention,

FIG. 2 is a diagrammatic representation of the complete suspensionsystem according to a second embodiment of the invention,

FIG. 3 is a schematic diagrammatic representation of part of a vehiclesuspension system according to a third embodiment of the presentinvention; and

FIG. 4 is a diagrammatic representation of part of a vehicle suspensionsystem according to a fourth embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a suspension system for the two rear wheels 8 a, 8b of a vehicle comprises a pair of suspension arms 10 a, 10 b, eachconnected near its inboard end 12 a, 12 b to a vehicle body 14 by arespective pivoting mounting 16 a, 16 b about which the suspension arm10 a, 10 b can pivot to allow the wheel 8 a, 8 b mounted at its outboardend 18 a, 18 b to move vertically relative to the vehicle body 16. Eachsuspension arm 10 a, 10 b is also connected to the body 14 by a spring20 a, 20 b towards its outboard end 18 a, 18 b.

The left suspension arm 10 a is also connected to the body 14 by ahydraulic strut 22 a at its inboard end 12 a, inboard of the mounting16a, and the right suspension arm 10 b is connected to the body 14 by anidentical hydraulic strut 22 b at a point outboard of the mounting 16 b.Therefore the points of connection between the struts 22 and thesuspension arms are both offset from the axes of the respective pivotsin the same direction, in this case to the same side of the vehicle. Thedistances 1 a, 1 b between the points of connection of the two struts 22a, 22 b and the respective pivots 16 a, 16 b are the same.

Each strut 22 a, 22 b comprises a cylinder 24 mounted on the body 14 anda piston 26 dividing the cylinder into a first working chamber 28 aboveit and a second working chamber 30 below it, the piston 26 beingconnected to the suspension arm 10 a, 10 b by means of a connecting rod32 extending down through the second chamber, and out of the bottom endof the cylinder 24. Each pair of corresponding chambers in the twocylinders is interconnected by a hydraulic pipe, i.e. the two firstchambers 28 are interconnected by a first pipe 34 and the two secondchambers 30 are interconnected by a second pipe 36, and each of thechambers 28, 30 and the pipes 34, 36 is filled with hydraulic fluid

In its simplest form, the hydraulic system described is closed so thatfluid can only flow between the two first chambers 28 and the two secondchambers 30. The hydraulic system then acts as a simple anti-rollmechanism. If the two wheels 8 a, 8 b move vertically in the samedirection the suspension arms 10 a, 10 b rotate in opposite directionsabout their respective pivots 16 a, 16 b, the two pistons 26 move inopposite directions, one of the struts 22 a, 22 b expanding and theother contracting, and fluid flows in one direction through the pipe 34and in the other direction through the pipe 36 and the system provideslittle resistance to the wheel movement. Because of the asymmetry of thestrut mounting arrangement which allows each chamber 28, 30 to beconnected to the corresponding chamber on the other strut 22 which hasan equal effective cross sectional area, equal movements of the wheelscan be accommodated by movement of fluid from one strut to the other.

It will be appreciated that, in order to allow for some simultaneousmovement of the two wheels 8 a, 8 b in the opposite vertical directions,i.e. to allow the vehicle to roll, in the type of closed systemdescribed above some mechanism must be provided to allow the combinedvolume of the two upper chambers 28 and the combined volume of the twolower chambers 30 to change thereby allowing the two struts 22 to expandor contract simultaneously and the suspension arms 10 to rotate in thesame direction. This could be done for example by allowing fluid toenter or leave each of the interconnecting pipes 34, 36 as required intosuitable accumulators against a resistive force the strength of whichwould determine the overall resistance of the system to roll.

The arrangement shown in FIG. 1 can also be incorporated into an activeroll control system by connecting each pair of interconnected chambersto a source of fluid pressure such as a hydraulic pump via a valve blockso that fluid pressure to each pair of chambers can be controlled.Increasing the pressure to the two first chambers 28 will cause the leftwheel 8 a to rise and the right wheel 8 b to drop relative to the body,thereby causing the vehicle to roll to the left, and increasing thepressure to the two second chambers 30 will cause the left wheel 8 a todrop and the right wheel 8 b to rise relative to the body, therebycausing the vehicle to roll to the right. FIG. 2 shows a suspensionsystem for a four wheeled vehicle according to a second embodiment ofthe invention in which the rear pair of wheels 108 a, 108 b and thefront pair of wheels 108 c 108 d are each supported on a suspensioncorresponding to that shown in FIG. 1.

In FIG. 2 parts of the rear suspension corresponding to those shown inFIG. 1 are given the same number but increased by 100, and parts of thefront suspension are given corresponding reference numbers but with theletters a and b replaced by c and d. The hydraulic lines 134, 136interconnecting the rear struts 122 a, 122 b , and the correspondinginterconnecting lines 142, 144 between the front struts 122 c, 122 d,are each connected to a valve block 140 which in turn is connected to ahydraulic pump 146. The valve block 140 includes an electronic controlcircuit which can allow independent control of the roll of the front andthe rear of the vehicle.

Whilst roll of the vehicle will require movement of hydraulic fluidbetween the interconnecting pipes 134, 136, 142, 144 and the valveblock, bump and rebound of the front pair of wheels or the rear pair ofwheels only requires movement through the interconnecting pipes 134,136, 142, 144. With the system controlling the front and rearsuspensions together and hydraulic interconnection of pipe 134 to pipe142 and of pipe 136 to pipe 144 through the valve block, the resistanceof the system to small scale bump and rebound movements is therefore lowwhich can improve the secondary ride quality of the vehicle whilstmaintaining the vehicle roll stiffness.

Referring to FIG. 3, in a third embodiment of the invention each of thesuspension arms 210 a, 210 b is turned upwards at its inboard end so asto form an L-shaped member, supported on a pivot 216 a, 216 b at thejunction between the horizontal part and the vertical part. The top ends212 a, 212 b of the vertical parts, which are directly above the pivots216 a, 216 b when the vehicle is level, are connected to the pistons 226of a pair of hydraulic struts 222 a, 222 b. The struts are horizontaland their cylinders 224 are both pivotably connected to the body 214 tothe same side of the respective suspension arm pivots 216. In thisexample only one hydraulic chamber 228 is shown for each strut, on theopposite side of the piston 226 to the connecting rod 232 to thesuspension arm 210 a, 210 b, and the two chambers 228 are interconnectedby a hydraulic line 234. The struts are of equal diameter and areconnected to the suspension arms 210 a, 210 b at equal distances fromthe axes of the respective pivots 216 a, 216 b. Clearly the struts couldeach have two chambers as in the first two embodiments.

In roll each of the suspension arms 210 a, 210 b rotates in the samedirection about their pivots 216 a, 216 b and the pistons 226 in thestruts 222 a, 222 b therefore move in the same direction. However thistends to either compress or expand the hydraulic fluid in the chambers228 and line 234 and is therefore resisted. On the other hand, inbounce, when the suspension arms 210 a, 210 b rotate in oppositedirections about their pivots 216 a, 216 b and the pistons 226 in thestruts 222 a, 222 b therefore move in opposite direction, the wheelmovement can be accommodated by movement of fluid from one strut to theother.

Referring to FIG. 4, a fourth embodiment of the invention is shown andidentical reference numerals are given to identical elements. ThisFigure is very similar to FIG. 3, but shows the connecting rodconnecting the piston to the body instead of the suspension arm, as withFIG. 3.

What is claimed is:
 1. A suspension system for a vehicle having a bodyand two wheels on opposite sides thereof, the system comprising a pairof suspension arms for supporting the two wheels, a pivot connectingeach suspension arm to the vehicle body, and a pair of struts eacharranged for connection between the vehicle body and one of thesuspension arms, at a respective distance from the pivot, to controlrotation of the suspension arm about its pivot thereby to controlvertical movement of the respective wheel relative to the vehicle body,wherein each strut comprises a cylinder and a piston which togetherdefine a working chamber having a volume, the piston having a workingarea and being movable relative to the cylinder to change the volume,the two working chambers are interconnected with each other; the strutsare asymmetrically arranged; and the cross sectional areas of thepistons and the distances between the struts and the respective pivotsare arranged such that equal vertical movements of the wheels in thesame direction produce equal but opposite changes in the volume of therespective working chambers.
 2. The suspension system according to claim1 wherein the pistons have equal working areas and the struts areconnected to the suspension arms at equal distances from the respectivepivots.
 3. The system according to claim 1 wherein each piston has afront side and a back side and the system further comprises a connectingrod extending from the back side of each piston connecting the piston toone of the body and the suspension arm, and the working chambers are onthe same side of the respective pistons.
 4. The system according toclaim 1 wherein each piston divides its cylinder into first and secondworking chambers, the two first working chambers having an identicalcross sectional area and being interconnected and the two secondchambers having an identical cross sectional area and beinginterconnected.
 5. The suspension system according to claim 4 furthercomprising a source of fluid pressure connectable to each pair ofinterconnected chambers, and control means arranged to control the flowof fluid to and from each pair of chambers to control actively roll ofthe vehicle.
 6. The suspension system according to claim 1 wherein thestruts are arranged such that expansion of one of them causes upwardmovement of its respective wheel relative to the body, and expansion ofthe other causes downward movement of its respective wheel relative tothe body.
 7. The suspension system according to claim 1 for a vehiclehaving a longitudinal axis, wherein the pivots have pivot axes which arearranged to be parallel to said longitudinal axis and the struts arearranged such that expansion of each of them causes rotation of therespective suspension arm in the same direction about its pivot.
 8. Thesuspension according to claim 7 wherein the struts are connected to thesuspension arms at points of connection which are both offset from thepivot axis of the respective suspension arm in the same direction. 9.The suspension system according to claim 8 wherein one of the struts isconnected to its suspension arm inboard of its pivot and the other isconnected to its suspension arm outboard of its pivot.
 10. Thesuspension system according to claim 8 wherein both the struts arearranged to operate in use in a substantially vertical direction and arearranged above the suspension arms.
 11. The suspension according toclaim 1 wherein both of the struts are arranged substantiallyhorizontally and act on the suspension arms at points above therespective pivot axes.
 12. The suspension system according to claim 1further comprising a source of fluid pressure to which at least one ofthe pairs of interconnected chambers is connected, and control meansarranged to control the flow of fluid to and from said pair of chambersto control actively roll of the vehicle.